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Ban on PFOS and Alternative Approaches for Fluorine-Containing Finishing Agents 【Abstract】PFOS has been banned by the EU as it is a PBT substance; it serves as a precursor for perfluorooctylsulfonamide-based finishing agents that provide water resistance, oil repellency, and easy cleanability. Regulations stipulate that its concentration in chemicals and formulations must not exceed 0.005%, which effectively means a ban on its use. This ban will take effect on June 27, 2008. Since such finishing agents are widely used to impart special functional properties to textiles, clothing, and leather, it is urgent to find alternatives to PFOS. Therefore, this article provides a detailed explanation of the mechanisms behind water and oil repellency, as well as the synthesis processes of intermediate and final products derived from PFOS and PFOA. From this, the main principles that should guide the search for alternatives can be understood, and an assessment of possible alternative approaches is given. 【Keywords】PFOS and PFOA; water-repellent, oil-repellent, and easy-to-clean finishes; relevant regulations; alternative approaches 【Chinese Library Classification Number】TS195·25 Document Code: A Article ID: 1005-9350(2008)03-0001-05 Water-repellent, oil-repellent, and easy-to-clean finishes are treatments applied to fabrics in order to alter their surface properties, thereby preventing water and oil from wetting the fabric easily and making it simpler to remove any contaminants that may adhere to it. Among them, the most effective are fluoride-containing finishing agents. In 2006, the consumption of fluorine-containing finishing agents in China’s dyeing and finishing industry was approximately 11,000 tons, with over 95% of these products being imported. The main brands included Unidyne (from Daikin in Japan), Asahiguard (from Asahi Glass in Japan), Nuva (from Hoechst in Germany), Scotchguard (from 3M in the United States), and Olephobol (from Clariant in Switzerland). The consumption is expected to reach 15,000 tons by 2010. The ban on perfluorooctanesulfonate (PFOS) and perfluorooctic acid (PFOA), as well as ammonium perfluorooctanic acid and ammonium perfluorooctanoate, will have a severe impact on fluorine-containing water-repellent, oil-repellent, and easy-to-clean finishing agents. Prohibitions on PFOS and PFOA 1·1 The EU’s prohibitions regarding PFOS (1) On December 5, 2005, the European Commission issued a regulation restricting the sale and use of PFOS, namely 2005/0244/COD, along with the final version COM(2005)618 final. This regulation was submitted for legislative approval; it represents an amendment to Directive 76/769/EEC, issued by the European Community on July 27, 1976, regarding the restriction of the use and sale of certain dangerous substances and preparations. To date, there have been over 40 amendments to this directive, which serve as the basis for assessments under the REACH regulation. The regulation stipulates that substances with a concentration of 0.1% or higher cannot be sold on the market or used as raw materials or components in various preparations. Appendix A of this decree specifies the chemical structural formula for PFOS as C8F17SO2X, where X can be OH, Metal Salt, Halide, Amide, or other derivatives; only when X is OH does it correspond to a Sulfonate. In practice, the water-repellent, oil-repellent, and easily cleanable finishing agents that use perfluorooctyl sulfamide derivatives are all based on perfluorooctanesulfonyl fluoride (C8F17SO2F), that is, Perfluorooctane Sulfonic Halide, rather than Perfluorooctane Sulfonate. (2) A notice on the official EU website regarding the recommendation adopted by the European Parliament on October 25, 2006, to impose restrictions on the sale and use of perfluorooctanesulfonic acid (PFOS). The law will become applicable in EU member states within 18 months and will officially take effect in mid-2008. The limits for PFOS are as follows: ① It may be used as a raw material and component in formulations when its mass fraction reaches or exceeds 0.005% (50 ppm) ； ②The limit for semi-finished products is 0.1% (100 ppm) ； ③The limit for textiles and coated materials is 1µg/m2 (this value must be divided by the weight of the textile in meters squared to convert it to mg/kg). (3) The European Parliament issued Directive 2006/122/FCOF on restricting PFOS on December 12, 2006. It reaffirmed the recommendation adopted by the European Parliament on October 25, 2006, regarding limits on PFOS; these recommendations are to become **law** in the member states by December 27, 2007, and shall come into force officially on June 27, 2008. The decree also mentions that PFOA and its salts are suspected to have similar risks to PFOS. 1.2 United States and other relevant bans: Around 2001, data provided by the U.S. Environmental Protection Agency (EPA) indicated that perfluorooctanesulfonyl compounds (PFOS) are highly persistent in the environment, accumulate there as well as in human and animal tissues, posing potential risks to human health and the environment. Production and use of PFOS were halted based on environmental management and human health; at that time, 3M Company’s Scotchguard FC series was also discontinued. Research by the U.S. Environmental Protection Agency shows that perfluorooctanoic acid (PFOA) and its salts are also types of organic polymers that are difficult to degrade; they exhibit high persistence in the environment, accumulate there, and build up in human and animal tissues. They can enter the food chain as well, posing potential risks to human health and the environment. Despite the considerable uncertainty currently surrounding the potential risks of PFOA and its salts to human health. Moreover, it has not yet been determined exactly how PFOA gets into the environment and how it causes harm to human health. The EPA believes that PFOA may be released during the production and processing of certain organic chemicals, and more scientific data is needed for risk assessment in order to decide whether to ban or restrict its use. Currently, the U.S. EPA has proposed a PFOA Stewardship Program, which aims to reduce PFOA emissions by 95% by 2010 and by 100% by 2015, meaning zero emissions. DuPont’s Teflon will reduce PFOA by over 97% by 2010. On July 6, 2005, Sweden issued notice G/TBT/N/SWE/51, stipulating that PFOS and substances that degrade into PFOS are prohibited from entering the Swedish market. 1.3 Hazards of PFOS: As research into the toxicology and ecology of PFOS progressed in various countries, the Organization for Economic Co-operation and Development (OECD) issued a risk assessment report on PFOS at the 34th meeting of its Chemicals Committee in December 2002, classifying it as a toxic chemical that is difficult to degrade and can accumulate in living organisms (referred to as a PBT substance). According to the OECD’s risk assessment, once organisms ingest PFOS, it distributes in the blood and liver; due to its high stability, it is likely to be difficult to break down through the organism’s metabolic processes. Of course, although quite slowly, PFOS can be excreted from the body through urine and feces. Its \"half-excretion time\" varies greatly among different species: rats require only 7.5 days, while it takes humans 8.7 years to eliminate it from the body. Therefore, PFOS has a high degree of bioaccumulation and various toxicities; it not only causes damage to the respiratory system but also leads to the death of newborn infants ； Animal experiments have shown that a concentration of 2 mg/kg of PFOS in the body can lead to death. The Scientific Committee on Health and Environmental Risks (abbreviated as SCHER) conducted a scientific review of the aforementioned assessments and confirmed on March 18, 2005, that PFOS is a highly persistent, bioaccumulative, and toxic chemical. To determine the hazards of PFOS, the UK’s Department for Environment, Food and Rural Affairs (Defra) conducted an independent PBT assessment of its hazards, and the results were completely consistent with those of the OECD assessment. PFOS also has the ability to migrate over long distances in the environment, resulting in widespread contamination. Recent water quality surveys in China have detected PFOS and PFOA in the Yangtze River and the Huangpu River; the concentration of PFOS in the Huangpu River was 26.46 mg/L, while that of PFOA was 159.83 mg/L, indicating pollution by PFOS in aquatic environments. According to predictions by international experts in environmental science, surfactants and finishing agents containing PFOS will be restricted for use worldwide within five years, until their use is completely banned. The top priority is to develop alternatives to PFOS and PFOA. Under the REACH regulation, in addition to registration, the use of Substances of Very High Concern (SVHC) requires authorization. SVHCs include substances that are carcinogenic, mutagenic, or toxic to the reproductive system ； Permanently persistent, bioaccumulative, and toxic substances ； Substances that are highly persistent, stable, and subject to high bioaccumulation ； Environmental hormones, etc. PFOS and PFOA are classified as SVHCs, and their derivatives must meet the requirements of the REACH regulation when entering the European market. The purpose of the authorization system is to ensure that such substances are increasingly replaced. Alternatives to waterproof, oil-repellent, and easy-to-clean finishing agents that contain PFOS and PFOA can be either fluorine-containing or non-fluorine-containing, but they must meet the mechanisms of waterproofing, oil repellency, and easy cleaning as well as certain relevant parameters; therefore, the key points of these mechanisms need to be clarified in this article. Regulations set minimum limits for PFOS and PFOA in both final products and intermediates. Questions arise as to how to ensure that these limits are not exceeded in alternatives, and whether PFOS and PFOA could exceed those limits as by-products when using their analogs as alternatives, or when considering the synthesis of such alternatives. In light of this, it is necessary to detail the entire synthesis process of PFOS and PFOA, as well as the finishing agents derived from them. 2 Properties of organic fluorides and water/oil repellent finishing 2·1 Properties of organic fluorides Fluorine is the element with the highest electronegativity in the periodic table, at 4.0. When hydrogen atoms on hydrocarbon chains are replaced by fluorine, the bond energy of C-H bonds increases from 416.7 kJ/mol to 485.3 kJ/mol for C-F bonds. Therefore, fluorosurfactants exhibit excellent chemical stability in strong acids and strong bases, and are highly stable at high temperatures, allowing them to be used at temperatures above 300°C. Since the covalent radius of a fluorine atom is 0.064 nm, which is half of the C-C bond length of 0.131 nm, a fluorine atom can effectively shield the carbon chain. Due to the short C-F bond length of 0.1317 nm (compared to 0.1766 nm for C-C bonds), the surface energy is low, resulting in an extremely low surface tension in aqueous solutions. Generally, surfactants dissolved in water can reduce the surface tension of water from 72.6 mN/m to around 30 mN/m, while fluorinated surfactants containing -CF or -CF2- groups can lower the surface tension of water to 10–15 mN/m. This significant reduction in surface tension occurs both in water and in oils, thereby granting them excellent hydrophobic and oleophobic properties. Furthermore, compared to hydrocarbon surfactants with the same carbon chain length, fluorinated surfactants reach saturation adsorption at much lower concentrations; as a result, their critical micelle concentration (CMC) is also much lower. This enables high efficacy at low concentrations – excellent results can be achieved even at very low concentrations, with surface tension being reduced to very low levels at 50–100 mg/L. 2·2 Mechanism of water and oil repellent finishing: Water-repellent finishing primarily aims to reduce the δc value on the fiber surface to a level lower than the surface tension of water. The δc of cellulose fibers is 200 mN/m, which is much higher than the surface tension of water; therefore, they are easy to wet. By adding surfactants, the surface tension of water is reduced, making it even easier for these fibers to be wetted. By using substances with a low critical surface tension and a high contact angle as water-repellent finishing agents to modify the fiber surface, satisfactory water repellency can be achieved. For example, the critical surface tensions of polydimethylsiloxane, polyfluoroacrylates, and polymethacrylates are 27 mN/m, 5 mN/m, and 47 mN/m respectively, all of which are lower than the surface tension of water; in particular, fluoropolymers exhibit a more significant water-repellent effect. Since capillary effects must be taken into account for breathable fabrics, these effects cause wetting, resulting in a water-repellent treatment value on the fabric surface that is about 20 mN/m higher than the δc value for the films listed above. For some water-repellent treatments, the δc value on cotton fibers changes due to capillary effects; for example, it increases to 38–50 mN/m for polydimethylsiloxane, and to 24–25 mN/m for polyfluoroacrylates, yet they still exhibit excellent water-repellent properties. The mechanisms of oil-repellent finishing and water-repellent finishing are very similar; both involve altering the surface properties of fibers to reduce the critical surface tension δc. However, water has high surface tension; after modification, a large contact angle can be achieved with waterproof finishing agents that have a very low δc, thereby providing a waterproof effect. However, for oils with lower surface tension (20–40 mN/m), it is necessary to reduce the critical surface tension δc of the modified fiber surface even further in order to achieve a larger contact angle and prevent the oil from wetting the fiber, thus achieving an oil-repellent effect. Existing perfluoroalkyl acrylate polymers all have very low δc values, enabling them to be both waterproof and oil-repellent.